The present invention relates to a magnetic tape and a method for producing same, and more particularly relates to the production of a magnetic tape adapted for high density magnetic recording such as magnetic sound recording and magnetic video recording.
It is well known in the field of magnetic recording that a thin structure combined with large coersive force and high residual magnetic flux density of the magnetic layer of a magnetic tape is a prerequisite to high density recording, i.e. short wave recording, by the magnetic tape.
In the case of the conventional magnetic tape in which a base tape film of synthetic resin is coated with a mixture of ferromagnetic material powder with a synthetic resin binder, it is difficult to make the magnetic layer, i.e. the mixture layer, thinner than a certain limit. Further, the use of a considerable amount of the binder in the magnetic layer makes it difficult to provide a large apparent coersive force and a high residual magnetic flux density. For these reasons, the conventional coated type magnetic tapes are quite unsuited for high density recording.
In order to respond to the increasing demand for high density recording, it has already been proposed, as a substitute for the conventional coated type magnetic film, to use a ferromagnet alloy film for the magnetic tape for high density recording. As such ferromagnet alloys, age-hardening type magnet alloys such as Alnico type magnets and Fe-Cr-Co type magnets have received much recognition because of their large coersive force and high residual magnetic flux density.
One process for producing such a magnet alloy film includes rolling of a cast ingot. In this case, however, the alloys have to be chosen only from a group suited for rolling. Extremely high workability is required for the material in order to laminate the material down to a film of several micronmeters by rolling. Even when the lamination is achieved successfully by rolling, there remains difficulty with subsequent thermal process such as age-hardening and solution treatment.
For production of the film of the above-described type, it is also proposed to blow molten magnet alloy onto a quench roll rotating at a high speed in order to form a film on the surface of the quench roll. In this case, however, it is almost impossible to form a film of uniform thickness at the level of several micronmeters suited for high density recording. Further, although this process removes the need for solution treatment, it still necessitates the subsequent age-hardening which is difficult to practice after the alloy has been extremely laminated to the level of several micronmeters. Therefore, although use of the age-hardening type magnet alloy enables production of an extremely laminated magnetic tape with large coersive force and high residual magnetic flux density, it is next to impossible to reduce the thickness of the magnetic tape beyond a certain limit because of difficulty in heat treatment. This naturally forms a limit to high density recording.
It was also proposed to form a thin layer of a magnetic material on a synthetic resin base film by plating or vacuum evaporation. This process enables an appreciable degree of lamination of the magnetic material. However, since the magnetic layer is formed on the base film made of synthetic resin, it is difficult to carry out the subsequent heat treatments smoothly. As a consequence, this process is unsuited for age-hardening type magnet alloys.